This project is defining at the protein level the molecular basis of heritable disorders of collagen metabolism that cause skeletal disease. The goal is to understand the consequences of mutations in collagen genes in terms of expressed protein structure and altered macromolecular interactions in the extracellular matrix. The specific aims include understanding the molecular effects of type II collagen defects that include amino acid substitutions caused by single base changes and full and partial exon deletions caused by splice site mutations. Rules in the relationship between underlying gene defect, expressed protein abnormality, tissue pathology and clinical phenotype will be explored. Changes in post-translational chemistry of collagen molecules bearing mutant chains, that is in proline hydroxylation, lysine hydroxylation, hydroxylysine glycosylation and intermolecular cross-linking will be examined, pursuing an hypothesis that the quality of such secondary changes are important determinants of the clinical phenotype and disease severity. The approach is to apply methods in protein analysis (peptide mapping and gas-phase sequencing adapted for the special features of collagen chemistry) to human tissue specimens. Tissues from defined cases of chondrodysplasia including achondrogenesis/hypochondrogenesis, spondyloepiphyseal dysplasia (SED), spondyloepimetaphyseal dysplasia (SEMD), Kniest dysplasia and familial osteoarthrosis/mild SED will be studied. Defects at the protein level in collagen types IX, X and XI will also be sought in the extracellular matrix using a similar approach. The nature of the collagen cross-linking defect in Ehlers-Danlos syndrome VI will be pursued. Common features of the pathology of bone matrix collagen in osteogenesis imperfecta will also be explored at the protein level. The significance of the work is the major impact collectively of overt heritable skeletal diseases, and also of related mild mutations and genetic polymorphisms that are strongly suspected to predispose to the common disorders of the aging skeleton, osteoporosis and osteoarthritis. With the increasing burden in life quality and health care delivery of degenerative disorders of the skeleton, understanding the molecular basis and prevalence of such genetic factors is essential if effective diagnostic, preventive and therapeutic strategies are to be pursued.